The closer to 1:1 that you get the ratio between drive pressure and boost, the more efficient your system is working.
Normally, with a single turbo setup you see somewhere in the neighborhood of 2:1 (drive:boost), or more. This isn't very efficient, causes a lot of stress on the turbo and doesn't result in the best EGT reduction.
Now, with a twin setup, you can get much closer to 1:1 (1.1 - 1.3:1 is pretty normal). This results in all much more of the exhaust energy being used, making power, and cooling EGT's.
The better you get that ratio, the more efficient your engine is working. Remember, an engine is just a big air pump.